As is known, these articles are obtained by laying a sheet of impermeable material over a sheet of permeable material (of non-woven fabric), with a padding consisting of an absorbent pad interposed between the two sheets. More specifically, both in the case of nappies of children and in the case of nappies for adults, it is usual to add accessory components such as lateral flaps for closing the nappy round the wearer's waist.
Generally speaking, in a prior art machine, the lateral closure flaps are applied along certain stretches of a continuous web of a material for making nappies, these stretches corresponding to the single nappies, when subsequently divided.
Patent application WO2010001361A1, in the name of the same Applicant as this invention, describes a machine for making absorbent articles of the above mentioned kind.
The machine comprises a unit for forming and applying pairs of ateral flaps to the continuous web.
This unit is equipped, at its upper end, with a device for cutting a continuous web of elatomeric material into suitably shaped single pieces constituting the lateral flaps for closing the nappies.
The cutting device is substantially tangent to a first and a second roller. The first and second rollers both have suction pads which pick up the single flaps cut by the cutting device in such a way as to form respective successions of single, equioriented flaps. Further, the suction pads are slidable between two end positions along, a direction parallel to the axis of the respective roller, in such a way as to space the single flaps by a length which is less than the transversal dimension of the continuous web of nappies.
The single flaps, conveyed one after the other from the first roller to the second, are transferred to the same receiving roller which is tangent to both of the rollers and located downstream of them.
The first and second rollers feed the respective single flaps to pairs of suctions seats on the receiving roller which thus form the pair of lateral flaps intended for each single nappy.
The suction seats on the receiving roller are also slidable along a direction parallel to the axis of the roller itself, in order to further space the single flaps until reaching the predetermined spacing along the waistline of the nappies.
Once the pairs of flaps formed have been further spaced by the receiving roller, they are transferred from the receiving roller to an accelerator roller which conveys each pair of lateral flaps in step and applies them to the continuous web.
Both the slidable pads of the first and second rollers and the slidable seats of the receiving roller are mechanically driven by cam means.
The size of a nappy defines the spacing of the lateral flaps and further defines the size of each single lateral flap.
In the unit of the type described, when the spacing of the lateral flaps varies, the length by which the slidable pads of the separating device and the suction seats of the receiving roller must be moved also varies.
The cam means which drive the slidable pads and the suction seats are limited in movement so that the spacing they can create according to the size of the nappy being made can only be varied to limited extents. More specifically, the cam means which create the lateral flap spacing for children's nappies cannot create the lateral flap spacing required for nappies to be used by adults.
As a result, changing over to making nappies of a different size necessitates substituting the first and second rollers of the separating device and the receiving roller for similar rollers equipped with cam means suitable for creating the spacing required by the size of the nappy to be made.
Moreover, the size of a single lateral flap, in particular the longitudinal length of the single flap, defines the size of the slidable pads and of the suction seats.
Since the slidable pads and the suction seats cannot be substituted when the longitudinal length of the lateral flap varies, changeover involves entirely substituting the rollers of the separating device and the receiving roller for similar rollers equipped with slidable pads and suction seats of suitable size. More specifically, increases in the longitudinal dimension of the lateral flaps mean increases in their radial dimension, which in turn means increases in the radial dimensions of the respective rollers.
As a result, when the size of the lateral flaps must be varied, it is necessary not only to substitute the rollers but also to vary the distance of the roller axes from each other so as to reposition them suitably according to their radial dimensions.
Repositioning the rollers is a structurally complex operation which involves extended machine downtimes, since the rollers of the separating device and the receiving roller are mechanically complex parts of considerable size.